1. Field of the Invention
The present invention relates to a key module, more particularly, to a key module with a multi-layer light guiding structure
2. Description of Prior Art
Portable electronic device such as mobile phones and personal digital assistants (PDA) are popular information appliances. In those portable electronic devices, keys are often used for user input interface to input data and select function of the electronic devices.
The key in the prior art electronic device generally comprises a backlight to provide illumination for user in dark environment. Therefore, user can correctly identify key. The conventional backlight comprises a transparent light guide and a light emitting diode (LED) in the electronic device. Light emitted from the LED is guided by the light guide to distribute over bottom of each key. Therefore, symbols or alphabet can be clearly displayed on the key.
The LED in backlight application is generally of mono color, therefore, symbols or alphabet formed on top of the key are printed with different color to provide colorful display effect. Alternatively, a multiple-color LED is used for a key when a specific color effect is demanded for the key. The manufacture time and cost for above two approaches are burden for the manufacturer.
As the progress of technology, the electronic device is also provided with more function for user. For example, mobile phone can be used for photo, game and video playback. However, the backlight in the mobile phone illuminates symbols and alphabet on all keys. Therefore, user cannot identify the key for game control, photo shooting or video playing and the user is liable to have wrong operation. Moreover, the mobile phone may be rotated during game control, photo shooting or video playing operation. The symbols and alphabet on the keys have different orientation and the user cannot identify the key for game control, photo shooting or video playing, especially when the symbols and alphabet on the keys are transparent.